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Abstract

In this work we present a LIDAR sensor devised for the acquisition of time resolved laser induced fluorescence spectra. The gating time for the acquisition of the fluorescence spectra can be sequentially delayed in order to achieve fluorescence data that are resolved both in the spectral and temporal domains. The sensor can provide sub-nanometric spectral resolution and nanosecond time resolution. The sensor has also imaging capabilities by means of a computer-controlled motorized steering mirror featuring a biaxial angular scanning with 200 μradiant angular resolution. The measurement can be repeated for each point of a geometric grid in order to collect a hyper-spectral time-resolved map of an extended target.

Time –Wavelength, false color, intensity distribution of the acquired optical signal for sample #1 (left side) and sample #2 (right side). The intensity scale is natural logarithmic and normalized for each sample to the maximum of the entire data set. The time Tm corresponds to the maximum of the measured temporal impulse response of the sensor.

Time resolved (solid line) and time averaged (dot line) spectra for samples #1 and #2, left and right side respectively. The time resolved spectra have been acquired at the indicated delays. Spectra are intensity normalized at unitary integral.

Fluorescence time-wavelength intensity distribution normalized at the maximum at each acquisition wavelength. The time Tm corresponds to the maximum of the measured temporal impulse response of the sensor.

Fluorescence intensity decay profiles at various acquisition wavelengths. Blue lines for sample #1 in band #1 (solid) and band #2 (dashed). Green lines for sample #2 in band #1 (solid) and band #2 (dashed). Black solid line for the system temporal impulse response for comparison. The plot reports the natural logarithm of data normalized to their maximum.

Spatial distribution of the ratio between the fluorescence intensity in the spectral bands #1 and #2. The fluorescence intensity was previously averaged over the full 80 ns measured time lapse. The ratio value corresponding to the black background was set to zero. Ratio for the G10 epoxy fiberglass slab and the Botticino sandstone slab are, respectively, 8.1 ± 0.2 and 3.0 ± 0.4 (mean ± std).

Spatial distribution of the time needed to reach e−4 of the maximum of fluorescence in the spectral band #1. The time constant for the background is set to zero. Time delays for the G10 epoxy fiberglass slab and the Botticino sandstone slab are, respectively, 42.5 ± 0.2 ns and 32.8 ± 1.6 ns (mean ± std).